The present invention relates to a method and apparatus for wastewater treatment which can efficiently treat wastewater discharged from semiconductor and liquid crystal plants and the like that contains fluorine in addition to organic substances, such as surface active agents and organic solvents, with a relatively small number of tanks required for such treatment.
The present invention also relates to a method and apparatus for wastewater treatment which can efficiently treat wastewater that contains hydrogen peroxide in addition to organic substances, with a relatively small number of tanks.
From the view points of statutory laws and regulations for water pollution control, in the case where the wastewater contains, in addition to fluorine, organic substances, such as surfactant and organic solvents, it is necessary to treat the fluorine and also the organic substances to a predetermined concentration level. The presence of such organic matter in wastewater causes an increase in chemical oxygen demand (COD) and/or biochemical oxygen demand (BOD). Therefore, organic matter such as surface active agents in the wastewater must be positively removed despite the fact that they are chemically different from fluorine.
Hitherto, it has been usual practice that a mixed type of wastewater which contains, in addition to fluorine, organic substances, such as surfactant and organic solvents, is treated in such a way that the fluorine is first chemically treated by a chemical such as slaked lime in a tank and then, in a separate tank, organic matter, such as surfactant and organic solvents, are treated by employing a biological treatment method and/or a physical treatment method, such as activated carbon adsorption. This method for fluorine treatment using chemicals such as slaked lime and the like involves addition of chemicals in the process of treatment and, therefore, the resulting treated water has high electric conductivity. Therefore, such treated water has not been recycled for supply to ultrapure water production equipment.
As a typical example of conventional apparatus for removal of fluorine in wastewater there has been known one shown in FIG. 15. This apparatus for fluorine removal is such that fluorine-containing wastewater is fed into two separate calcium carbonate-packed tanks 533A and 533B for fluorine treatment therein (Japanese Patent Application Laid-Open No. 5-253576).
In this fluorine removal apparatus, fluorine-containing wastewater is fed into the calcium carbonate-packed tanks 533A and 533B for two-stage treatment, and outflow water is introduced into a circulation tank 542. The water under treatment in the circulation tank 542 is introduced into a membrane separation unit 543 in which the water is separated into condensed water containing calcium carbonate crystals flowed out of the second-stage calcium carbonate-packed tank 533B and membrane-permeated water. The condensed water is returned to the circulation tank 542. A part of the condensed water is returned to the first-stage calcium carbonate-packed tank 543A.
According to the arrangement of this fluorine removal apparatus, fluorine in the wastewater is immobilized to the calcium carbonate in the calcium carbonate-packed tanks 533A and 533B so that it is changed into calcium fluoride. After the lapse of a predetermined time period of treatment, such calcium fluoride is removed from the calcium carbonate-packed tanks 533A and 533B.
As another type of fluorine removal apparatus there has been known a calcium fluoride collecting apparatus as shown in FIG. 16 (Japanese Patent Application Laid-Open No. 5-254829). In this calcium fluoride collecting apparatus, a calcium carbonate reaction tank 644, or a reaction tank for reaction operation with respect to calcium fluoride, includes steam piping 647 which functions as a heating device, a blower 639 which functions as an air feeder device, and an aeration pipe 602. The calcium carbonate reaction tank 644 may include a vacuum deaerator (not shown).
Specifically, the calcium fluoride collecting apparatus incorporates a technique such that a supply of calcium carbonate from a calcium carbonate silo 646 is added to a fluorine-containing solution, the solution being then subjected to high temperature treatment at temperatures of 50 to 100.degree. C., hot air through-flow treatment, and/or hot vacuum deaeration treatment, whereby calcium fluoride is collected.
In the case where the object for treatment is organic matter-containing fluorine wastewater, such a fluorine removal apparatus as described above is incorporated, as shown by reference numeral 770 in FIG. 17, for example, into a wastewater treatment system 780 for treating organic matter-containing fluorine wastewater produced in a production room 731 of a semiconductor plant.
Generally, in a production room 731 of a semiconductor plant which fabricates integrated circuits (ICs) and the like, there is installed a so-called etching device 737 as shown in FIG. 17. The etching device 737 involves use of an etching agent composed principally of hydrogen fluoride and/or ammonium fluoride.
With recent microstructure oriented development in the manufacture of ICs, there has been a growing tendency toward the use of etchants with an organic substance, typically surfactant included therein. Therefore, etching device 737 discharges organic matter-containing fluorine wastewater into wastewater treatment system 780.
Separately from etching device 737, an organic solvent consuming unit 732 exists within production room 731. Organic solvent consumption unit 732 is an organic solvent user such that it cleans the surface of a wafer with an organic solvent and dries the same. Organic solvent consumption unit 732 discharges organic solvent-containing wastewater. This organic solvent-containing wastewater is also introduced into the wastewater treatment system 780 for treatment therein. That is, the organic solvent-containing wastewater discharged from the organic solvent consumption unit 732 is also directed through a pipe 726 to flow into a raw water tank 735.
Thus, the organic solvent-containing wastewater and the fluorine-containing wastewater, combined together into organic matter-containing fluorine wastewater, flow through pipe 726A for entry into raw water tank 735. Then, the wastewater is pumped by a raw water tank pump 736 to flow through pipe 726B for being introduced upward into a fluorine removal unit 770. A treating tank 733 of the fluorine removal unit 770 is packed with calcium carbonate mineral. In treating tank 733, therefore, fluorine in the wastewater reacts with the calcium carbonate mineral to form calcium fluoride. Therefore, by separating calcium fluoride from the wastewater it is possible to remove fluorine present in the wastewater.
Aforesaid fluorine removal unit 770 is almost incapable of removing organic matter, such as surfactant and organic solvents. The wastewater which has been treated in the fluorine removal unit 770 is caused to flow into a precipitation tank 713 through a pipe 727. The concentration of fluorine in the precipitation tank 713 is detected by a fluorine concentration meter 715. Organic matter concentration in the settling tank 713 is comparatively high. Therefore, the wastewater is introduced from the precipitation tank 713 into a typical biological treatment unit 740 for biological treatment of organic matter, such as surfactant and organic solvents.
In FIG. 17, acid type exhaust gases from the etching device 737 are treated by acid scrubber 734, while organic exhaust gases from organic solvent consumption device 732 are treated in activated carbon adsorption columns 738A, 738B.
Next, description is given of a conventional wastewater treatment apparatus for treating hydrogen peroxide wastewater from semiconductor and/or liquid crystal plants which contains organic matter, such as surface active agents and organic solvents.
In case where wastewater contains, in addition to hydrogen peroxide, organic substances, such as surfactant and organic solvent, both the hydrogen peroxide and the organic substances cause an increase in COD (chemical oxygen demand) in the wastewater. Therefore, it is necessary that hydrogen peroxide and organic matter, such as surfactant and organic solvent, in the wastewater must be surely removed. In the past, such organic matter-containing hydrogen peroxide wastewater has been treated in such a way that first, hydrogen peroxide is catalytically treated with activated carbon or the like and then organic matter, such as surfactant and organic solvent, are treated in a separate tank.
Hitherto, a hydrogen peroxide removal apparatus for removing hydrogen peroxide in wastewater of the type shown in FIG. 19 has been known wherein hydrogen peroxide is catalytically treated with granular activated carbon (Japanese Patent Application Laid-Open No. 6-91258). This hydrogen peroxide removal apparatus 870 includes a treating tank 833 comprising a catalytic zone 911 partitioned by a bottom wire mesh 905 and a peripheral wall 906 and open upward, and a sedimentation zone 912 surrounding the outer side of the catalytic zone 911 with the peripheral wall 906 placed therebetween. At lower peripheral locations there are provided an opening 904 which allows the sedimentation zone 912 to be kept in communication with the catalytic zone 911, and a feed port 903 for enabling wastewater to horizontally flow into the catalytic portion 911. In operation, granular activated carbon is previously placed into the catalytic zone 911 in a quantity range of 1 to 35% of the effective tank capacity of the catalytic zone 911.
In that condition, hydrogen peroxide-containing wastewater from a pipe 807A is introduced into the treating tank 833 through the feed port 903 at the tank bottom. The hydrogen peroxide-containing wastewater flows into the catalytic zone 911 through the wire mesh 905 to fill the catalytic zone 911. Meanwhile, from a branched pipe 807B and through the horizontal feed port 904 is introduced hydrogen peroxide-containing wastewater (the flow rate of which is adjustable by a valve 920) into the catalytic zone 911. As a consequence, within the catalytic zone 911 there occurs an eddy current along with an upward current so that the granular activated carbon comes in contact with the hydrogen peroxide-containing wastewater, whereby the hydrogen peroxide in the wastewater is decomposed into water and hydrogen by the catalytic action of the activated carbon. The wastewater which has undergone such treatment overflows the edge of the catalytic zone 911 into the sedimentation zone 912 and is discharged from a discharge port 918 provided behind a baffle plate 917 via a pipe 827. In this case, some part of the granular activated carbon may overflow along with post-treatment wastewater into the sedimentation zone 912, but the so overflown granular activated carbon is allowed to be detained and precipitated for a while, being then returned to the catalytic zone 911 through the opening 907. Therefore, only supernatant is discharged from a discharge port 918 of the sedimentation zone 912.
A hydrogen peroxide removal apparatus is often incorporated in a wastewater treatment system 1080, as illustrated in FIG. 18, for example, for treating organic matter-containing hydrogen peroxide wastewater generated at a production room 1031 of a semiconductor plant.
Generally, in a production room 1031 of a semiconductor plant which manufactures ICs (integrated circuits) and the like, a large number of manufacturing units are installed, including RCA cleaning unit 1037 which performs so-called RCA cleaning process, and organic solvent utilization unit 1032 for use of organic solvents, such as acetone and isopropyl alcohol. Aforesaid RCA cleaning process is a cleaning technique developed by RCA Consumer Electronics and typically comprises a first step of removing organic matter by using NH.sub.4 OH, HCl, and H.sub.2 O, and a second step of removing alkali metal and/or heavy metal by using HCl, H.sub.2 O.sub.2, and H.sub.2 O. With recent microstructure oriented development in the manufacture of ICs, there has been an increased tendency toward inclusion of surface active agents in above said NH.sub.4 OH and HCl. Organic matter-mixed wastewater from RCA cleaning unit 1037 or the like which contains hydrogen peroxide and organic substances, such as surfactant and organic solvent, flows through a pipe 1026 into a raw water tank 1035 in which the wastewater is adjusted in both quantity and quality to a certain measure.
On the other hand, organic matter-containing wastewater from the organic solvent utilization unit 1032 flows into the raw water tank 1035 through a pipe 1026A. Therefore, the hydrogen peroxide-containing wastewater and the organic matter-containing wastewater meet into a combined stream in the pipe 1026A so that they are present as organic matter-containing hydrogen peroxide wastewater in the raw water tank 1035.
Next, the wastewater is introduced by a raw water pump 1036 into a hydrogen peroxide removal unit 1070 via a pipe 1026B. Hydrogen peroxide in the wastewater is decomposed into oxygen and water within a tank 1033 of the hydrogen peroxide removal unit 1070. In this hydrogen peroxide removal unit 1070, however, it is almost impossible to remove organic matter, such as surfactant and organic solvent. As such, the wastewater which has undergone aforesaid treatment is introduced into the treating tank 1028 through a pipe 1027. The concentration of hydrogen peroxide in the treating tank 1028 is detected by a oxidation-reduction potentiometer 1034. In case that the wastewater in the treating tank has a high concentration of hydrogen peroxide, the wastewater is introduced into a biological treatment unit (not shown) for treatment of organic matter.
Meanwhile, as FIG. 18 shows, exhaust gas emitted from RCA cleaning unit 1037 and/or organic solvent utilization unit 1032 which contains organic substances (organic matter-containing exhaust gas) is treated by a treating system 1090 for organic matter-containing exhaust gas as provided separately from the treating system 1080 for organic matter-containing hydrogen peroxide wastewater.
Reference characters 1038A and 1038B designate activated carbon adsorption columns.
As earlier stated, at contemporary semiconductor plants where fabrication of ICs is becoming more and more microstructure-oriented, there is a growing tendency that organic matter such as surfactant and organic solvent get mixed in fluorine wastewater. The reason is that as ICs go more microstructural, greater need does exist for improvement of cleaning technique and, therefore, that it is a recent practice to mix organic matter, such as surface active agents, into cleaning agents and/or etching agents in order to obtain increased cleaning effect and/or etching effect.
Therefore, it is necessary that fluorine wastewater and organic matter-mixed wastewater containing surfactant, organic solvent, etc. must be treated in economical and rational way.
However, as already mentioned, in the past, fluorine and organic matter, such as surfactant in wastewater have been treated in separate tanks. More specifically, in the above described prior art treating arrangement, two separate apparatuses are required, namely, fluorine removal apparatus and biological treatment apparatus for treatment of organic matter. Where two different treatment tanks are separately installed, the problem is that high initial cost is required.
As FIG. 17 illustrates, at production room 731 of a semiconductor plant, etching unit 737 and other production units, and organic solvent utilization unit 732 are installed in large numbers. Along with recent trend that the fabrication of ICs is becoming more microstructure-oriented, it is now general practice that organic matter, such as surface active agent, is mixed into an etching agent which contains fluorine, and/or that chemicals containing an organic solvent are used in cleaning and drying operations. Therefore, in mixed types of wastewater which contain these chemicals (fluorine and organic substances, such as surfactant and organic solvents), organic substances present in wastewater are on the increase with time in quantity.
However, with prior art fluorine removal devices shown in FIGS. 15 and 16, and another prior art fluorine removal device 770 shown in FIG. 17, the problem is that such device, itself alone, is almost incapable of dealing with organic matter, such as surfactant and organic solvents.
The reason is that any of the prior art fluorine removal devices is unfit for microbial propagation and has no function to perform biological treatment, the device being operated in such a condition that no effect could be expected of the device for treatment of organic matter such as surfactant and organic solvents.
With reference to hydrogen peroxide wastewater, there is also a growing tendency that, at contemporary semiconductor plants, organic substances, such as surface active agents and organic solvents, mix into such wastewater. In view of the fact that microstructure-oriented IC production becomes more and more prominent, it is necessary to improve the cleaning technique accordingly. As such, there is a growing need for rational treatment of organic matter-mixed hydrogen peroxide wastewater of the kind generated at production room 1031 of a semiconductor plant as shown in FIG. 18, that is, hydrogen peroxide wastewater containing organic substances, such as surface active agents and organic solvents.
However, as already mentioned, it has hitherto been common practice that hydrogen peroxide is exclusively treated in one decomposition tank (hydrogen peroxide removal unit 1070) in which the hydrogen peroxide is catalytically decomposed with activated carbon into water and oxygen gas. Meanwhile, organic matter, such as surface active agent and organic solvent, are biologically treated alone, or subjected to physical adsorption treatment in an activated carbon adsorption column. Anyway, organic substances, such as surface active agent and organic solvent, in wastewater are treated separately from hydrogen peroxide. Therefore, two types of apparatuses are required, namely, apparatus for removal of hydrogen peroxide and apparatus for biological treatment of organic substances. This involves the problem of high initial cost.
As FIG. 18 illustrates, at production room 1031 of a semiconductor plant, there are present production related units including RCA cleaning unit 1037, and organic solvent utilization unit 1032 in large numbers. Further, for the convenience of productive operations, hydrogen peroxide and other chemicals containing organic matter, such as surfactant and organic solvent, are used for cleaning purposes. Therefore, production room 1031 generates wastewater of the sort in which hydrogen peroxide and organic matter, such as surfactant and organic solvent, are mixed together.
However, the above described conventional hydrogen peroxide removal unit 1070 involves the problem that it is almost incapable of independently performing the task of treating organic matter, such as surfactant and organic solvent. The reason is that the hydrogen peroxide removal unit 1070 does not permit propagation of microorganisms on the granular activated carbon because of the sterilizing action of hydrogen peroxide and, therefore, cannot be utilized for microbial treatment through propagation of microorganisms on the activated carbon.